Make your own illusion, and then see how many people are fooled by it.

All you need for this is a piece of paper, a black marker, and a ruler.

Look at the second illusion on Illusion 33 - (Which is longest?) You are going to draw your own version of this.

On the paper, draw two straight lines that are just the same length. Use the ruler to make sure that the lines are the same length. Put them a couple of inches apart.

Now add short lines at the top and bottom of the lines, like the letter V - for the long line on the right, make it look like arrows pointing up and down. For the other line, make the points of the V's start at each end of the long line. Check what you have drawn against the example, to make sure your V's are pointed the right way.

Now take a look at what you have drawn. Even though **you know** the two long lines are the same length, one line looks shorter than the other. That’s the illusion.

**Now for the experiment**. Let’s see how many people can see that both lines are the same. When you show it to someone, ask them, “Which line is longer?”

Keep track of how many say -

- the line on the left is longer
- the line on the right is longer
- both lines are the same length

How many boys get it right? How many girls get it right? Are girls better than boys at this? Do more older kids get it right, or are younger kids better at this?

If you show it to both kids and adults, who is better at seeing that it is an illusion?

After people guess which line is longer, you can let them use a ruler to prove to themselves that the lines are the same length.

Here’s another illusion you can learn how to draw yourself (thanks to Michael Sibbernsen, one of the Kids Pages' visitors).

DevilsFork_508.pdf (http://www.niehs.nih.gov/assets/files/devilsfork_508.pdf) (874KB)

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